The multi-input multi-output (MIMO for short) technique is a wireless transmission technique using multiple (NT) transmitting antennas and multiple (NR) receiving antennas. It can effectively improve the capacity and the link transmission performance of a wireless network. MIMO channels (represented by a matrix HNT, NR) formed by NT transmitting antennas and NR receiving antennas can be divided into NS independent channels, and the value range of NS is [1, NmaxS], where NmaxS=min{NT, NR}. The value of NS is determined by the relativity of the MIMO channels. The greater the relativity of the MIMO channels is, the smaller the value of NS is; the smaller the relativity of the MIMO channels is, the greater the value of NS is. In a Long Term Evolution (LTE for short) system, NS at a User Equipment (UE for short) side is referred to as a rank, NS at a network side is referred to as a layer.
There are mainly two approaches for implementing the MIMO technique: spatial diversity and spatial multiplexing. In the LTE system, for the spatial multiplexing mode, the UE needs to feed back ranks of the MIMO channels to the network side, which performs rank self-adaptation processing based on the ranks fed back by the UE. A simple rank self-adaptation processing method is that the network side controls the number of the independent channels sending downstream data based on the newly reported rank (NS) at the UE side. As the ranks of the MIMO channels change slowly, this method enables the network side to effectively self-adapt the rank change of the MIMO channels. However, when the ranks of the MIMO channels change quickly (e.g., when the UE is in a high-speed moving state), the difference between the newly reported rank at the UE side used by the network side and the rank of the current actual MIMO channel may be greater such that spatial advantages of the MIMO will be given a great discount.